A wide variety of substituted amidines are disclosed in the patent literature. For example:
U.S. Pat. No. 3,903,163 (1975), discloses N,N'-disubstituted 2-naphthyleneacetamidines having activity as anti-depressants, anti-anxiety or calming agents. The N,N'-substituents are C.sub.1 -C.sub.3 alkyl. See also U.S. Pat. No. 4,134,992 (1979).
U.S. Pat. No. 3,972,931 (1976), discloses N,N'-disubstituted benzamidines as antidepressants, anti-anxiety and calming agents. The benzene radical is substituted in the 3- and/or 4-position by a halogen and the N,N'-substituents are C.sub.1 -C.sub.3 alkyl . See also U.S. Pat. No. 3,988,474 (1976).
U.S. Pat. No. 3,934,020 (1976), discloses N,N'-dialkyl-2-halophenylacetamidines as antidepressants and anti-anxiety agents. The benzene radical is substituted in the 3- and/or 4-position by halogen or CF.sub.3 and the N,N'-substituents are C.sub.1 -C.sub.3 alkyl. See also U.S. Pat. No. 3,983,250 (1976).
U.S. Pat. No. 2,221,280 (1938), discloses acetamidines which can be used to make alkylated or aralkylated amidines. These compounds reportedly can be used as textile agents, pesticides, bactericides and fungicides. The amidine starting compounds are preferably aryl amidines.
U.S. Pat. No. 596,797 (1897), discloses dialkoxyphenylamidines as local anesthetics.
U.S. Pat. No. 2,004,994 (1933), discloses diaryl acetamidines having utility as therapeutic agents. One aryl is substituted by a 2-ethoxy and a 5-phenyl group and the other aryl group is substituted in the 4-position with ethoxy or carbethoxy and the 3-position is optionally substituted by phenyl.
U.S. Pat. No. 3,632,593 (1972), discloses N-aryl-substituted aromatic amidines which are useful as analgesics, anti-inflammatory agents, neurosedative agents and hypotensive agents.
U.S. Pat. No. 4,503,076 (1985), discloses N-(2,6-dichlorophenyl)acetamidine as a vasodilator antihypertensive agent.
U.S. Pat. No. 3,906,044 (1975), discloses adamantylamidines and their use as antiviral agents. The adamantyl radical, which is optionally substituted by alkyl groups, can be directly linked to the carbon atom of the amidine or linked through a methylene linkage.
See also U.S. Pat. Nos. 4,183,957 (1980), 3,284,289 (1966), 3,678,109 (1972), 3,689,675 (1972), 3,729,565 (1973), 3,888,927 (1975).
U.S. Pat. No. 4,709,094 (1987), discloses N,N'-disubstituted guanidine derivatives which exhibit high binding activity with respect to the sigma receptor having the formula (I): ##STR2## wherein R and R' are an alkyl group of at least 4 carbon atoms, a cycloalkyl group of 3-12 carbon atoms, or carbocyclic or aryl, of at least 6 carbon atoms.
Two of the novel N,N'-disubstituted guanidines disclosed therein are also claimed therein viz., 1,3-di-(4-halo-2-methylphenyl)-guanidine and 1,3-di-(4-[.sup.3 H]-(2-methylphenyl)-guanidine.
Also claimed therein is a method of determining the relationship of abnormal psychotic-like behavior in a mammal displaying such behavior to sigma receptor system dysfunction, which comprises administering to the mammal displaying such behavior a water-soluble N,N'-disubstituted-guanidine which displaces in vitro N,N'-di-(4-[.sup.3 H]-2-methylphenyl)-guanidine bound to mammalian brain membrane, in an amount effective to alter the sigma brain receptor-modulated mental activity of the mammal and a method of treating a human being suffering from a psychotic mental illness associated with hallucinations, which comprises administering thereto a water-soluble N,N'-di-substituted guanidine which is an antagonist to the sigma receptor binding activity of a hallucinogenic benzomorphan, in an amount effective to ameliorate the hallucinations.
In U.S. Pat. No. 4,709,094 is further disclosed a method of determining the sigma brain receptor binding activity of an organic compound which comprises the steps of a) contacting in an aqueous medium a known amount of isolated mammalian brain membrane which has sigma receptor-like binding activity, with a mixture of (i) a tritium labeled N,N'-disubstituted guanidine which selectively binds sigma brain receptors, in a known amount capable of being bound to the sigma receptors of that brain membrane; and (ii) varying known amounts of a water soluble organic compound to be assayed for sigma receptor binding activity; b) separating the brain membrane from the tritium labeled compound which is not bound to the brain membrane in step a); and c) determining, from the molar relationship of the proportion of bound tritium-labeled compound which is separated in step b) to the molar amount of the organic compound employed in step a), the sigma receptor binding activity of that organic compound.
Certain benzomorphan opiates, such as N-allyl-normetazocine (SKF 10,047) and cyclazocine, in addition to analgesia, cause hallucinations, depersonalization, drunkenness and other psychotomimetic effects in man. In monkeys, dogs and rodents the psychotomimetic opiates cause behavioral and autonomic effects that are unlike those observed with administration of classical opiates such as morphine or the opioid peptides. Specific sigma "opioid" receptors in the brain are believed to mediate such atypical effects. Martin et al., J. Pharmacol. Exp. Ther. 197:517-532 (1976). It is believed that the sigma receptors also mediate some of the psychotomimetic effects of phencyclidine [PCP, angel dust], or alternatively, that psychotomimetic opiates act at specific PCP receptors. Zukin, R. S. et al., Mol. Pharmacol. 20:246-254 (1981); Shannon, H. E., J. Pharmacol. Exp Ther. 225:144-152 (1983); White, J. M. et al., Psycho-pharmacology 80:1-9 (1983); and Zukin et al., J. Neurochem. 46:1032-1041 (1986). PCP is a drug of abuse that causes a behavioral syndrome in man similar to that which is observed in schizophrenic psychosis. Aniline, O. et al., CRC Critical Rev. Toxicol. 10:145-177 (1982). Because of the potent psychotomimetic effects of sigma opiates and PCP, it is believed that sigma (and/or PCP) receptors play a role in mental illness, particularly schizophrenia.
A systematic investigation of the role of sigma receptors in normal and abnormal brain function has been hindered by a lack of specific sigma receptor binding assays and bioassays. Development of such specific assays requires well-characterized, highly selective and potent sigma receptor ligands. Recent studies have shown that brain membrane receptors can be labeled in vitro with (.+-.)[.sup.3 H]SKF 10,047, Su, T. P., J. Pharmacol. Exp. Ther. 223:284-290 (1982); (+)[.sup.3 H]SKF 10,047, Tam, S. W. et al., Proc. Natl. Acad. Sci. U.S.A. 81:5618-5621 (1984); Martin et al., J. Pharmacol. Exy. Ther. 231:539-544 (1984); and Mickelson, M. M. et al., Res. Commun. Chem. Pathol. Pharmacol. 47:255-263 (1985), although not selectively, Gundlach et al., Eur. J. Pharmacol. 113:465-466 (1985); and Largent, B. L. et al., J. Pharmacol. Exp. Ther. ZLB: 739-748 (1986), and with (+)[.sup.3 H]3-(3-hydroxyphenyl)-N-(1-propyl)-piperidine ((+)[.sup.3 H]3-PPP), Largent et al., Proc. Natl. Acad. Sci. U.S.A. 81:4983-4987 (1984), which is apparently more selective for sigma receptors than the others.
After the initial in vitro studies by Martin et al ., (1976) supra, Keats and Telford (Keats, A. S. et al., "Analgesics: Clinical Aspects." In Molecular Modification in Drug Design, R. F. Gould (ed.), Advances in Chemistry Series #45 Amer. Chem. Soc., Wash. D.C. (1964)), and Haertzen (Haertzen, C. A. Cyclazocine and Nalorphine on the Addiction Research Center Inventory (ARCI), Psychopharmacologia (Berl.) 18:366-377 (1970)), numerous investigators set out to biochemically characterize the different opiate receptors (mu receptors, kappa receptors and sigma receptors) in vitro.
The first evidence for the existence of a separate sigma receptor in test tube experiments was provided by Su (1982) supra in a paper describing an etorphine-inaccessible binding site in guinea pig brain membranes which was apparently selectively labeled by tritium-labeled SKF-10,047. To overcome the fact that SKF-10,047 could label multiple opioid receptors in the brain, Su performed his receptor binding assay using tritium labeled SKF-10,047 in the presence of excess unlabeled etorphine. Etorphine is a very strong opiate agonist drug which is known to bind to delta receptors, mu receptors and kappa receptors with almost equal potency. Su used etorphine to saturate all mu, kappa and delta receptors in a brain membrane preparation and then added tritium labeled SKF-10,047. This enabled him to detect a sigma binding site that was apparently different from mu, kappa and delta receptors.
A major breakthrough in identifying the sigma receptor as a separate entity occurred when Tam et al. (1984), supra, demonstrated that the previous problems in selectively labeling the sigma receptor were caused by the fact that in all previous experiments a racemic SKF-10,047 preparation was used. Tam showed that using a tritium labeled (+)-SKF-10,047 isomer one could selectively label a sigma receptor that was different from the mu, delta and kappa opioid receptors. On the other hand, Tam showed that (-)-SKF-10,047 apparently labeled the mu and kappa receptors but not the sigma receptors. Tam, S. W., Eur. J. Pharm. 109:33-41 (1985). This finding has now been confirmed. (Martin et al., 1984, supra). Moreover, there is evidence from behavioral experiments, Khazan et al., Neuropharm. 23:983-987 (1984); Brady et al., Science 215:178-180 (1981), that it is the (+)-SKF-10,047 isomer that is solely responsible for the psychotomimetic effects of SKF-10,047.
One of the most important findings of the biochemical characterization of the sigma receptor has been that this receptor binds all synthetic opiate drugs that are known to have hallucinogenic and psychotomimetic effects. Opiates that do not have psychotomimetic effects in vivo do not bind to this receptor. Most importantly, it has been shown that besides hallucinogenic opiate drugs, the sigma receptor also binds many antipsychotic drugs that are used clinically to treat hallucinations in schizophrenic patients. (Tam and Cook, 1984). The initial observations with regard to antipsychotic drug binding to the sigma receptor (Su, 1982) were subsequently extensively confirmed and extended by Tam et al. (1984), supra, also showed that when one used radioactively labeled haloperidol, one of the most potent antipsychotic drugs that is used clinically, about half of the binding sites in brain membrane preparations are actually sigma receptors whereas the other half of the binding sites are apparently dopamine receptors. It has long been known that most antipsychotic drugs are also dopamine receptor antagonists. Previously, the beneficial actions of antipsychotic drugs in psychotic patients have been attributed to the dopamine receptor-blocking effect of these drugs. It is clear from the work by Tam, however, that numerous clinically used antipsychotic drugs also bind to the sigma site. All antipsychotic drugs that bind to the sigma receptor may in part cause the beneficial effect of alleviating hallucinations through the sigma receptor. Taken together all these observations suggest the sigma receptor as a prime candidate to be involved in the pathogenesis of mental illness, particularly schizophrenia in which hallucinations are a major clinical symptom.
Deutsch, S. I. et al. (Clinical Neuropharmacology, Vol. 11, No. 2, pp. 105-119 (1988)) provided a review of the literature which implicates the sigma receptor site in psychosis and anti-drug efficacy. According to Deutsch et al., certain benzomorphans which possess analgesic potency in humans are also associated with a high incidence of psychotomimetic effects. It has now been concluded that the analgesic action is associated with the levorotatory isomers of racemic mixtures of the benzomorphans, while the psychotomimetic effects are attributable to the dextrorotatory isomers in the racemic mixtures. See Haertzen, C. A., Psychopharmacologia 18:366-77 (1970), and Manallack, D. T. et al., Pharmacol. Sci. 7:448-51 (1986). Coupled with the fact that many of the in vivo effects of these dextrorotatory enantiomers and the binding of dextrorotatory tritiated SKF-10,047 are not antagonized by naloxone or naltrexone, these data strongly support the concept that the psychotomimetic effects of the dextrorotatory enantiomers are associated with the sigma receptor binding site.
Further, Su, T. P. et al. (Life Sci. 38:2199-210 (1986)), and Contreras, P. C. et al. (Synapse 1:57-61 (1987)), have proposed the existence of endogenous ligands for the sigma receptor, suggesting that the dysregulation of the synthesis, release, or degradation of these natural ligands may be a naturally occurring mechanism of psychosis. Accordingly, sigma receptor antagonism provides the potential for an effective antipsychotic therapeutic treatment. See Ferris, R. M. et al., Life Sci. 38-2329-37 (1986), and Su, T. P., Neurosci. Let. 71:224-8 (1986).
As further evidence of the role of the sigma receptor in psychosis, the substituted carbazole cis-9-[3-(3,5-dimethyl-1-piperazinyl)-propyl]carbazole dihydrochloride (rimcazole) was identified as a potential antipsychotic agent based on its ability to antagonize apomorphine-induced mesolimbic behaviors selectively without altering the intensity of stereotypic behaviors. Further, the compound does not accelerate the rate of dopamine synthesis and does not affect dopamine-stimulated production of CAMP in homogenates of rat striatum and olfactory tubercle, thus establishing that rimcazole does not exert its action at the level of post-synaptic dopamine receptors in the mesolimbic area.
Rimcazole is able to competitively inhibit the specific binding of dextrorotatory tritiated SKF-10,047, the prototype sigma receptor agonist, suggesting that rimcazole acts at the sigma receptor site. Rimcazole, therefore, shows potential antipsychotic activity in humans, without extrapyramidal effects, pharmacological behavior which is consistent with its role as a competitive antagonist of the sigma-receptor.
Another compound, BMY 14802, has demonstrated many properties in preclinical behavioral tests which suggest its efficacy as a potential antipsychotic agent which is devoid of extrapyramidal side effects. The compound (1) did not cause catalepsy in rats; (2) does not inhibit the binding of [.sup.3 H]spiperone to the D.sub.2 class of striatal dopamine receptors in rats; (3) did not increase the maximal density of the (.sup.3 H]spiperone-labeled D.sub.2 site in striatum even following chronic administration (20 days) to rats; (4) does not appear to interact with the D.sub.1 subclass of dopamine receptors; and (5) does not inhibit dopamine-stimulated CAMP production or the binding of [.sup.3 H)SCH 23390 in vitro. These data suggest that BMY 14802 has a low potential for production of tardive dyskinesia and further suggests that the antipsychotic effects would be mediated by a nondopaminergic site. Further, BMY 14802 binds with relatively high affinity to the sigma receptor, with the binding being stereoselective (the dextrorotatory enantiomer being 10 times more potent at inhibiting binding than the levorotatory enantiomer). BMY 14802 does not bind to the adrenergic, muscarinic, cholinergic, or histaminergic sites, suggesting that the compound would not be associated with unpleasant sedative and autonomic side effects.
Accordingly, compounds which bind selectively to the sigma receptor site and which antagonize this site may be expected to be useful antipsychotic drugs which are devoid of extrapyramidal effects.
The antipsychotic and anti-schizophrenia drugs that are currently in use have very strong side effects that are mainly due to their action on dopamine receptors. The side effects often involve irreversible damage to the extrapyramidal nervous system which controls movement functions of the brain. Patients under long term antischizophrenic drug treatment often develop a syndrome that involves permanent damage of their ability to control coordinated movement.
The foregoing studies have shown that the sigma binding site has the characteristics of 1) stereo-selectivity towards dextrorotatory benzomorphan opiates and insensitivity for naloxone; 2) high affinity for haloperidol and moderate to high affinity for phenothiazine antipsychotic drugs which are also known to be potent dopamine receptor blockers; and 3) insensitivity for dopamine and apomorphine. This intriguing drug selectivity profile calls for a thorough analysis of the role of sigma receptors in normal and abnormal brain function. In order to do so, it is essential that a spectrum of highly selective and potent sigma receptor active compounds be available.
Fear, or apprehension, is characterized by the anticipation of a known danger or event. In contrast, neurotic anxiety is characterized by an apprehension with no known cause, or a maladaptive response to a trivial danger. In recent years, generalized anxiety disorder (GAD) has been characterized by psychiatrists as being chronic (continually present for at least 1 month) and exemplified by three of four psychomotor symptoms: motor tension, autonomic hyperactivity, apprehensive expectation, and vigilance and scanning. Before this characterization was adopted, clinical trials of anxiolytic agents in the United States occurred in patients which were described variously as suffering from anxiety neurosis, anxiety with associated depression, and other such terms. Anxiety disorders affect 2-3% of the general population (the 67 million prescriptions written in 1977 for just two popular anxiolytics confirm this projected incidence). The popularity of anxiolytics attests to their ability to ameliorate the debilitating symptoms of the disease. Taylor, D. P., FASEB J. 2: 2445-2452 (1988).
Historically, anxiety has been treated by agents including alcohol, opiates, and belladonna, which have a sedative component to their action. In the 20th century novel chemical entities were discovered which are safer for the treatment of anxiety including barbiturates, propanediol carbamates, and benzodiazepines. The pharmacological profiles of these drugs have suggested that their actions are mediated by receptors for .gamma.-aminobutyric acid (GABA). Although the benzodiazepines present a safer alternative than meprobamate and phenobarbital, they also are sedatives. In addition, the benzodiazepines control convulsions and produce muscle relaxation, properties that are unneeded or undesirable in the treatment of anxiety. Furthermore, these drugs can interact with alcohol, with potentially disastrous consequences. Recently, it has been appreciated that the benzodiazepines produce habituation and possess a pronounced liability, for example, withdrawal symptoms after chronic use. The need for anxioselective drugs that are more selective, have fewer side effects, and present a profile consistent with safety during protracted treatment has resulted in a continuing search for such drugs. This search has led to the synthesis and evaluation of agents that possess no obvious homology with the benzodiazepines. Taylor et al., supra.
Buspirone (Buspar) was the first novel anxiolytic to be approved for clinical use in the United States since the benzodiazepines were introduced almost 30 years ago. The introduction of buspirone into clinical trials for the treatment of anxiety was a direct result of its efficacy in a predictive animal model for the disease--the taming of the aggressive response of rhesus monkeys to the introduction of foreign objects into their cages according to the protocol described by Tompkins, E. C. et al., Res Commun. Psychol. Psychiatry Behav., 5:337-352 (1980). See Taylor et al., supra.
The preclinical screening of putative anxiolytics is dependent upon animal tests. Most of the laboratory data on new putative anxiolytics come from animal tests from two main classes. The first group of tests are based on conflict or conditioned fear. The second group of tests are based upon anxiety generated by novel situations. Although these tests differ in the way anxiety is produced, there has been surprising agreement amongst them in the classification of drugs as anxiolytic or anxiogenic. See File, S. E., TINS 10:461-463 (1987).
In two particular tests for anxiolytic activity, it is assumed that the anticipation of punishment causes a reduction in a response associated with the punishment. Conversely, anxiolytic agents that reduce anxiety result in an increased response rate. In the Geller-Seifter test, the rat receives food reward for pressing a lever, but also receives an electric foot shock, which has the effect of suppressing the response. This punished schedule alternates with an unpunished schedule wherein electric footshocks are not administered. During this unpunished schedule, lever-pressing is still rewarded. In the Vogel test, a rat is allowed to drink water, but also receives an electric shock through the water spout or the bars of the floor. In both the Vogel and Geller-Seifter tests, a measure of unpunished response is obtained in order to allow assessment of any non-specific stimulant or sedative drug effects or any changes in food or water intake. In both of these tests, benzodiazepines enhance the response rate in the punished periods, without increasing the rate of response in the absence of shock. While these tests are valid tests of anxiety, the only means of assessing them has been pharmacological. Taylor et al., supra.
A less widely used test utilizes punished locomotion, wherein a measure of unpunished crossing is obtained according to the rate at which a mouse crosses from one metal plate to another, wherein footshocks are administered whenever the mouse crosses. Although less widely utilized to test anxiolytic agents, this test has been able to detect drug-induced increases and decreases in anxiety by manipulating the shock level. File, S. E., J. Neurosci Methods 2:219-238 (1980).
The social interaction test of anxiety (File, supra; Jones, B. J. et al., Br. J. Pharmacol. 93: 985-993 (1988) exploits the uncertainty and anxiety generated by placing rats in an unfamiliar environment and in bright light. The dependent variable is the time that pairs of male rats spend in active social interaction (90% of the behaviors are investigatory in nature). Both the familiarity and the light level of the test arena may be manipulated. Undrugged rats show the highest level of social interaction when the test arena is familiar and is lit by low light. Social interaction declines if the arena is unfamiliar to the rats or is lit by bright light. Anxiolytic agents prevent this decline. The overall level of motor activity may also be measured to allow detection of drug effects specific to social behaviors.
The social interaction test of anxiety is one of the few animal tests of anxiety that has been validated behaviorally. Other behavioral measures indicative of anxiety and stress (e.g. defecation, self-grooming and displacement activities) were correlated with the reductions in social interaction; and other causes of response change (e.g. exploration of the environment, odor changes) were excluded. In order to validate the test physiologically, ACTH and corticosterone levels and changes in hypothalamic noradrenaline also were measured. File, TINS 10: 461-463 (1987).
Another test of anxiety that exploits the anxiety generated by a novel situation is the elevated plus maze. In this test, the anxiety is generated by placing the animals on an elevated open arm. Height, rather than the light level, is responsible for generating behavioral and physiological changes. The apparatus is in the shape of a plus with two open and two enclosed arms. The rat has free access to all arms on the apparatus. Anxiolytic activity may be measured by the percentage increase in the time that the test animal spends on the open arms and the number of entries onto the open arms. This test has also been validated behaviorally and physiologically.
Other agents which have been determined to have anxiolytic activity include the carbazole derivative 9-[3-(3,5-cis-dimethylpiperazino)-propyl]carbazole having the Formula (II): ##STR3## and pharmaceutical compositions thereof. See U.S. Pat. No. 4,400,383 (1983).
Serotonin receptor antagonists are also known to be useful for the treatment of anxiety. See Kahn, R. S. et al., J. Affective Disord, 8:197-200 (1987); Westenberg, H. G. M. et al., Psychopharmacol. Bull. 23:146-149 (1987).